Why Support the Three Arches of the Foot?

By Mark Charrette, DC

The feet are the foundation of support for the pelvis and spine. They provide the necessary stability to perform daily activities. Central to the success of the pedal foundation is its arched structure, which is actually a complex of three bony arches: the medial longitudinal arch, the lateral longitudinal arch and the anterior transverse (metatarsal) arch.

An evaluation of the anatomy and structure of the foot reveals that these three arches form a plantar "vault."1 This architectural design optimizes strength, permits sufficient flexibility to accommodate changes in terrain, and provides propulsion for locomotion. The foot's arched structure is not present at birth, but develops during childhood, by age 6 or 7 in most people.2

Because the feet are under continuous gravitational pressure when bearing the body's weight, breakdown in any of these three arches can result in abnormal gait and transmission of asymmetrical forces into the pelvis and spine. Let's briefly examine the functional capabilities of the three arches individually, and then address the effects of arch dysfunction and what can be done to support a collapsed arch.

Medial Longitudinal Arch

The most obvious arch is seen along the medial aspect of the foot. The navicular bone forms the "keystone" of this large and long arch, which is supported primarily by the plantar fascia and spring ligament.3 Nearly half a century ago, John Basmajian, MD (the "father of electromyography"), demonstrated that the muscles of the foot and lower leg do not provide support for the medial arch, except during toe-off when walking or while standing on tip-toe. He said, "From the present study, one may conclude that in the standing-at-ease posture muscle activity is not required and the muscles are inactive."4

While Basmajian believed in 1963 that he had settled the controversy regarding active (muscular) versus passive (ligamentous) support for the medial arch, there still remains much misinformation and persistent, misguided attempts at "strengthening muscles to rebuild the arch."

The most effective method for evaluating the function of the connective tissues that support the medial arch is to perform a comparison between its non-weight-bearing and weight-bearing alignments. The procedure is called the "navicular drop test," and was first described by Brody.5 This easy-to-perform clinical test objectively documents the presence (or absence) of collapse of the medial longitudinal arch, and has been used successfully to evaluate the risk of athletes with ACL ruptures.6

Lateral Longitudinal Arch

This arch is located along the outside of each foot. Because the cuboid bone serves as its structural keystone, the lateral arch relies much less on connective tissues for its support. For this reason, proper function of the lateral arch is extremely dependent on the alignment of the cuboid, which is frequently found to be in need of adjustment. Proper support for this arch is at least as important as for the other two, but is surprisingly absent in many orthotics.

Anterior Transverse (Metatarsal) Arch

This arch extends from the metatarsal heads back to the tarsal bones, and runs from the medial to the lateral sides of the foot. At its most anterior portion, the metatarsal heads contact the ground. Poor function and loss of this arch will often result in a build-up of thick callus underneath the metatarsal heads. Recurrent "dropped" metatarsal heads and/or irritation of one of the interdigital nerves (a "Morton's neuroma") is also a good indications that this arch is not being supported properly by the plantar fascia.

Static and Dynamic Support With Orthotics

The structural design of the three-arched plantar vault is very good at supporting weight and carrying high loads, while remaining flexible. During normal standing, the load of the body is balanced over the center of the foot, anterior to the ankle. This places the greatest amount of load at the apex of the three arches. This force is then distributed along the "buttresses" of the arches to the heel (which bears 50 percent to 60 percent of body weight) and the metatarsal heads (which bear 40 percent to 50 percent of body weight). Loss of this configuration will result in abnormal force concentrations, which will eventually cause degenerative and symptomatic clinical conditions.

During gait, the foot undergoes substantial changes. The arches and connective tissues must sustain the stress of heel strike, then adapt to the ground during stance phase, and finally become a rigid lever to provide an efficient push-off. This must all occur in a coordinated manner, with no glitches or hang-ups. The foot must permit a smooth transfer of the body's center of mass over the leg to conserve energy and keep the work expenditure to a minimum.7 The heavier a patient is, the greater the stresses on the feet and ankles.

Collapse or dysfunction of any of the arches needs to be addressed with flexible, custom-made stabilizing orthotics that will support the patient's foot both during standing (static support) and throughout the gait cycle (dynamic support), while controlling the impact forces. Particularly when there is asymmetry between the feet, arch problems can cause abnormal rotational forces to be transmitted into the pelvis and spine, resulting in chronic spinal symptoms. For this reason alone, doctors of chiropractic need to be aware of the status of their patients' three arches, since they can have a substantial impact on spinal health.

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